THALLIUM FILMS ON BICRYSTAL SUBSTRATES

ALL "ACTIVE" SUPERCONDUCTING DEVICES, SUCH AS MAGNETIC FIELD DETECTORS WITH ULTIMATE SENSITIVITY (SQUIDS) AND HIGH-SPEED COMPUTER LOGIC CIRCUITS ARE BASED ON JOSEPHSON JUNCTIONS. A JUNCTION IS MADE BY BRINGING TWO SUPERCONDUCTORS INTO WEAK CONTACT, BUT THIS HAS BEEN DIFFICULT USING HIGH-TEMPERATURE SUPERCONDUCTORS. THE BEST ENGINEERED JUNCTIONS MADE SO FAR IN HIGH-TEMPERATURE SUPERCONDUCTORS HAVE BEEN IN YTTRIUM MATERIALS GROWN ON BICRYSTAL SUBSTRATES; THE CRYSTAL GRAIN BOUNDARIES IN THE SUBSTRATE CONTROL THE LOCATION OF THE GRAIN BOUNDARIES IN THE SUPERCONDUCTING FILM. HOWEVER, THE RANDOMLY OCCURRING NATURAL GRAIN BOUNDARIES IN THALLIUM MATERIALS GIVE BETTER JUNCTION BEHAVIIOR THAN GAIN BOUNDARIES IN YTTRIUM. MOST LABORATORIES HAVE AVOIDED WORKING WITH THALLIUM BECAUSE OF ITS TOXICITY, BUT SUPERCONDUCTOR TECHNOLOGIES, INC., HAS BECOME A LEADER IN DEVELOPMENT OF THALLIUM MATERIALS. IN THIS CONTRACT STI WILL MAKE ENGINEERED JUNCTIONS BY GROWING HIGH-QUALITY THALLIUM SUPERCONDUCTORS ON BICRYSTAL SUBSTRATES.